public function getInstance($urlCon = null, $user = null, $pass = null)
 {
     if (FALSE == self::$carregada) {
         if (NULL == self::$con) {
             self::$con = new PDO($urlCon, $user, $pass);
         }
         self::$carregada = TRUE;
         return self::$con;
     }
     return self::$con;
 }